Chemoselectivity regioselectivity

However, the particular usefulness of enzymes stems from their selectivity. There are three types of selectivity exerted by enzymes chemoselectivity, regioselectivity, and stereoselectivity. 

Homogeneous transition-metal catalysts are usually chosen because of their high selectivity. A distinction is made between chemoselectivity, regioselectivity, and stereoselectivity, of which a special form is enantioselectivity. The latter is e.specially important in the production of pharmaceuticals. 

The Lipoarabinomannan Components of the Cell Wall Complex of Mycobacterium tuberculosis NPOEs in Chemoselective, Regioselective and Three-Component Double Differential Clycosidations... 

Chemoselectivity, regioselectivity, and diastereoselectivity in benzonitrile oxide cycloadditions... 

Key to these applications has been the control of selectivity-chemoselectivity, regioselectivity, diastereoselectivity, and, especially, enantioselectivity. Here the design of chiral catalysts, begun already in the 1960s, has allowed access to one product when multiple products would, in the past, have been expected. Both electronic and steric control are important, and different metal ions with their associated chiral ligands can have unexpected effects. 

The chemoselectivity, regioselectivity, diastereoselectivity, and enantioselectivity of heteroatom oxidations, epoxidations and CH insertions by dioxiranes have been reviewed.26 The selective ring-opening reactions of epoxides at high pressures have been reviewed (in Japanese).27... 

Aspects of selectivity in reaction pathways may be considered under the following topic areas chemoselectivity, regioselectivity, protection and, finally, stereoselectivi ty. 

Alkenylsilanes, mainly vinyl silanes and allyl silanes or related compounds, being widely used intermediates for organic synthesis can be efficiently prepared by several reactions catalyzed by transition-metal complexes, such as dehy-drogenative silylation of alkenes, hydrosilylation of alkynes, alkene metathesis, silylative coupling of alkenes with vinylsilanes, and coupling of alkynes with vinylsilanes [1-7]. Ruthenium complexes have been used for chemoselective, regioselective and stereoselective syntheses of unsaturated products. 

Selectivity comes in three sorts chemoselectivity, regioselectivity, and stereoselectivity. Chemoselectivity is which group reacts regioselectivity is where it reacts. Stereoselectivity is how the group reacts with regard to the stereochemistry of the product. 

Selectivity could be of different type—chemoselectivity, regioselectivity, enantioselectivity, etc. Reactions 1.11-1.13 are representative examples of such selectivities taken from homogeneous catalytic processes. In all these reactions, the possibility of forming more than one product exists. In reaction 1.11 a mixture of normal and isobutyraldehyde rather than propane, the hydrogenation product from propylene, is formed. This is an example of chemoselectivity. Furthermore, under optimal conditions normal butyraldehyde may be obtained with more than 95% selectivity. This is an example of regioselectivity. Similarly, in reaction 1.12 the alkene rather than the alcohol functionality of allyl... 

B. M. Trost has enunciated a set of criteria by which chemical processes can be evaluated. They fall under two categories selectivity and atom economy. The atom economy has already been discussed in section 1.4. The issues of selectivity can be categorized under the following headings chemoselectivity, regioselectivity, diastereoselectivity and enantioselectivity. 

What is an ideal or viable synthesis, and how does one approach a synthetic project The overriding concern in a synthesis is the yield, including the inherent concepts of simplicity (fewest steps) and selectivity (chemoselectivity, regioselectivity, diastereoselectivity, and enantioselectivity). Furthermore, the experimental ease of the transformations and whether they are environmentally acceptable must be considered. 

The reactions which have been reported are listed in Table 1 along with representative catalysts. In the presence of the appropriate ligand and under suitable conditions, many of the reactions proceed with a surprising chemoselectivity, regioselectivity, and enantioselectivity. The main side reactions are the isomerization of the primary hydrovinylation product or its further reaction with a second molecule of ethylene and the oligomerization or polymerization of the individual alkenes. These side reactions frequently become of significance only after the consumption of one of the reacting alkenes or at elevated temperatures. The hydrovinylation products are presented briefly below and this is followed by a more detailed discussion of the enantioselective control. 

Like chemoselectivity, regioselectivity is also governed largely by steric factors, with attack occurring preferentially at the least hindered epoxide center. This generalization holds true even for reactions performed in the presence of BP3-OEt2. However, stereoelectronic factors predominate in reactions of cyclic epoxides, which generally proceed predictably in a rrans-diaxial fashion. 

For a broader application of these new metal catalyzed [3+2]-cycloadditions in organic syntheses it is necessary that substituted methylenecyclopropanes react chemoselectively, regioselectively and if possible stereoselectively in this manner. The codimerizations of methylenecyclopropane itself described above indicate that the course of these cycloadditions is extremly sensitive to a number of influences... 

The apphcation of these types of ionic hquids as reagents and solvents for the chemoselective, regioselective, and stereoselective syntheses of 1,2- or 1,3-bro-moesters from aromatic aldehydes and 1,2- or 1,3-diols at room temperature has been studied (Fig. 12.63). Good to excellent yields and moderate enantiomeric excesses were obtained under these reaction conditions. 

Introduction Chemo-, Regio-, and Stereoselectivity Chemoselectivity Controlling Chemoselectivity Regioselectivity Markovnikov Hydration Mercuration-reduction Wacker oxidation... 

Classify the following reactions as chemoselective, regioselective or stereoselective reactions. 

Chemoselective, regioselective and E-stereoselective SN2 displacement with 1,3-chirality transfer by organocyanocopper-trifluoroborate. 

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